jarsigner - Unix, Linux Command

NAME

SYNOPSIS

DESCRIPTION

The
jarsigner tool is used for two purposes:

Tag

Description

1.

to sign Java ARchive (JAR) files, and

2.

to verify the signatures and integrity of signed JAR files.

The JAR feature enables the packaging of class files, images,
sounds, and other digital data in a single file for faster and
easier distribution. A tool named
jar enables developers to
produce JAR files.

A digital signature is a string of bits that is computed from some
data (the data being "signed") and the private key of an entity (a
person, company, etc.). Like a handwritten signature, a digital
signature has many useful characteristics:

Tag

Description

o

Its authenticity can be verified, via a computation that uses
the public key corresponding to the private key used to
generate the signature.

o

It cannot be forged, assuming the private key is kept secret.

o

It is a function of the data signed and thus cant be claimed
to be the signature for other data as well.

o

The signed data cannot be changed; if it is, the signature
will no longer verify as being authentic.

In order for an entitys signature to be generated for a file, the
entity must first have a public/private key pair associated with
it, and also one or more certificates authenticating its public
key. A certificate is a digitally signed statement from one
entity, saying that the public key of some other entity has a
particular value.

jarsigner uses key and certificate information from a keystore to
generate digital signatures for JAR files. A keystore is a
database of private keys and their associated X.509 certificate
chains authenticating the corresponding public keys. The
keytool utility is used to create and administer keystores.

jarsigner uses an entitys private key to generate a signature.
The signed JAR file contains, among other things, a copy of the
certificate from the keystore for the public key corresponding to
the private key used to sign the file.
jarsigner can verify the
digital signature of the signed JAR file using the certificate
inside it (in its signature block file).

At this time,
jarsigner can only sign JAR files created by the JDK
jar tool or zip files. (JAR files are the same as zip files,
except they also have a
META-INF/MANIFEST.MF file. Such a file
will automatically be created when
jarsigner signs a zip file.)

The default
jarsigner behavior is to sign a JAR file. Use the
-verify option to instead have it verify a signed JAR file.

Compatibility with JDK 1.1

The
keytool and
jarsigner tools completely replace
the
javakey tool provided in JDK 1.1. These new tools provide more
features than
javakey, including the ability to protect the
keystore and private keys with passwords, and the ability to
verify signatures in addition to generating them.

The new keystore architecture replaces the identity
database that
javakey created and managed. There is no
backwards compatibility between the keystore format and
the database format used by
javakey in 1.1. However:

Tag

Description

o

It is possible to import the information from an
identity database into a keystore, via the
keytool -identitydb command

o

jarsigner can sign JAR files also previously signed
using
javakey

o

jarsigner can verify JAR files signed using
javakey Thus, it recognizes and can work with
signer aliases that are from a JDK 1.1 identity
database rather than a JDK 1.2 keystore.

The following table explains how JAR files that were
signed in JDK 1.1.x are treated in the Java 2 Platform.

If an identity/alias is mentioned in the policy
file, it must be imported into the keystore for the
policy file to have any effect on privileges
granted.

1.

If an identity/alias is mentioned in the policy
file, it must be imported into the keystore for the
policy file to have any effect on privileges
granted.

2.

The policy file/keystore combination has precedence
over a trusted identity in the identity database.

3.

Untrusted identities are ignored in the Java 2 platform.

4.

Only trusted identities can be imported into Java 2 SDK
keystores.

Keystore Aliases

All keystore entities are accessed via unique aliases.

When using
jarsigner to sign a JAR file, you must
specify the alias for the keystore entry containing the
private key needed to generate the signature. For
example, the following will sign the JAR file named
MyJARFile.jar, using the private key associated with
the alias
duke in the keystore named
mystore in the
"working" directory. Since no output file is specified,
it overwrites
MyJARFile.jar with the signed JAR file.

Keystores are protected with a password, so the store
password (in this case
myspass) must be specified. You
will be prompted for it if you dont specify it on the
command line. Similarly, private keys are protected in a
keystore with a password, so the private keys password
(in this case
dukekeypasswd) must be specified, and
you will be prompted for it if you dont specify it on
the command line and it isnt the same as the store
password.

Keystore Location

jarsigner has a
-keystore option for specifying the name
and location of the keystore to be used. The keystore is
by default stored in a file named
.keystore in the
users home directory, as determined by the
user.home system property.

Note that the input stream from
the -keystore option is passed to the
KeyStore.load method.
If NONE is specified as the URL, then a null stream is passed
to the
KeyStore.load method. NONE should be specified if the
KeyStore is not file-based, for example, if it resides on a
hardware token device.

Keystore Implementation

The KeyStore class provided in the
java.security package supplies well-defined
interfaces to access and modify the information
in a keystore. It is possible for
there to be multiple different concrete
implementations, where each
implementation is that for a particular type of keystore.

Currently, there are two command-line tools that make
use of
KeyStore: keytool and
jarsigner, and also a
GUI-based tool named
policytool. Since
KeyStore is
publicly available, JDK users can write additional
security applications that use it.

There is a built-in default implementation, provided by
Sun Microsystems. It implements the keystore as a file,
utilizing a proprietary keystore type (format) named
"JKS". It protects each private key with its individual
password, and also protects the integrity of the entire
keystore with a (possibly different) password.

Keystore implementations are provider-based. More
specifically, the application interfaces supplied by
KeyStore are implemented in terms of a "Service Provider
Interface" (SPI). That is, there is a corresponding
abstract
KeystoreSpi class, also in the
java.security package, which defines the Service Provider Interface
methods that "providers" must implement. (The term
"provider" refers to a package or a set of packages that
supply a concrete implementation of a subset of services
that can be accessed by the Java Security API.) Thus, to
provide a keystore implementation, clients must
implement a provider and supply a
KeystoreSpi subclass
implementation, as described in
How to Implement a Provider for the Java Cryptography Architecture.

Applications can choose different types of keystore
implementations from different providers, using the
getInstance factory method supplied in the
KeyStore class. A keystore type defines the storage and data
format of the keystore information, and the algorithms
used to protect private keys in the keystore and the
integrity of the keystore itself. Keystore
implementations of different types are not compatible.

keytool works on any file-based keystore implementation.
(It treats the keytore location that is passed to it at
the command line as a filename and converts it to a
FileInputStream, from which it loads the keystore
information.) The
jarsigner and
policytool tools, on the
other hand, can read a keystore from any location that
can be specified using a URL.

For
jarsigner and
keytool, you can specify a keystore
type at the command line, via the
-storetype option. For
policytool, you can specify a keystore type via the
"Change Keystore" command in the Edit menu.

If you dont explicitly specify a keystore type, the
tools choose a keystore implementation based simply on
the value of the
keystore.type property specified in the
security properties file.
The security properties file
is called
java.security, and it resides in the
security properties directory,
java.home/lib/security, where
java.home is the
runtime environments directory
(the jre directory in the SDK or the
top-level directory of the Java 2 Runtime Environment).

Each tool gets the
keystore.type value and then examines
all the currently-installed providers until it finds one
that implements keystores of that type. It then uses the
keystore implementation from that provider.

The
KeyStore class defines a static method named
getDefaultType that lets applications and applets
retrieve the value of the
keystore.type property. The
following line of code creates an instance of the
default keystore type (as specified in the
keystore.type property):

KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());

The default keystore type is "jks" (the proprietary type
of the keystore implementation provided by Sun). This is
specified by the following line in the security
properties file:

keystore.type=jks

To have the tools utilize a keystore implementation
other than the default, change that line to specify a
different keystore type.

For example, if you have a provider package that
supplies a keystore implementation for a keystore type
called "pkcs12", change the line to

keystore.type=pkcs12

Note: case doesnt matter in keystore type designations.
For example, "JKS" would be considered the same as
"jks".

Supported Algorithms and Key Sizes

At this time,
jarsigner can sign a JAR file using either

Tag

Description

o

DSA (Digital Signature Algorithm) with the SHA-1
digest algorithm, or

o

the RSA algorithm with the MD5 digest algorithm.

That is, if the signers public and private keys are DSA
keys,
jarsigner will attempt to sign the JAR file using the
SHA-1/DSA algorithm. If the signers keys are RSA keys,
jarsigner will sign the JAR file using the MD5/RSA
algorithm. This is only possible if there is a
statically installed provider supplying an
implementation for the MD5/RSA algorithm. (There is
always a SHA-1/DSA algorithm available, from the default
"SUN" provider.)

The Signed JAR File

When
jarsigner is used to sign a JAR file, the output
signed JAR file is exactly the same as the input JAR
file, except that it has two additional files placed in
the
META-INF directory:

Tag

Description

o

a signature file, with a
.SF extension, and

o

a signature block file, with a
.DSA extension.

The base file names for these two files come from the
value of the
-sigFile option. For example, if the option
appears as

-sigFile MKSIGN

the files are named
MKSIGN.SF and
MKSIGN.DSA.

If no
-sigfile option appears on the command line, the
base file name for the
.SF and
.DSA files will be the
first 8 characters of the alias name specified on the
command line, all converted to upper case. If the alias
name has fewer than 8 characters, the full alias name is
used. If the alias name contains any characters that are
not allowed in a signature file name, each such
character is converted to an underscore ("_") character
in forming the file name. Legal characters include
letters, digits, underscores, and hyphens.

The Signature (.SF)
File

A signature file (the
.SF file) looks similar
to the manifest file that is always included
in a JAR file generated by the
jar tool. That
is, for each source file included in the JAR
file, the
.SF file has three lines, just as in
the manifest file, listing the following:

o

the file name,

o

the name of the digest algorithm used
(SHA), and

o

a SHA digest value.

In the manifest file, the SHA digest value for
each source file is the digest (hash) of the
binary data in the source file. In the
.SF file, on the other hand, the digest value for
a given source file is the hash of the three
lines in the manifest file for the source
file.

The signature file also, by default, includes
a header containing a hash of the whole
manifest file. The presence of the header
enables verification optimization, as
described in JAR File Verification.

The Signature Block (.DSA) File

The
.SF file is signed and the signature is
placed in the
.DSA file. The
.DSA file also
contains, encoded inside it, a certificate
authenticating the public key corresponding to
the private key used for signing.

JAR File Verification

A successful JAR file verification occurs if the
signature(s) are valid, and none of the files that were
in the JAR file when the signatures were generated have
been changed since then. JAR file verification involves
the following steps:

Tag

Description

1.

Verify the signature of the
.SF file itself.

That is, the verification ensures that the
signature stored in each signature block (.DSA)
file was in fact generated using the private key
corresponding to the public key whose certificate
also appears in the
.DSA file. It also ensures that
the signature is a valid signature of the
corresponding signature (.SF)
file, and thus the
.SF file has not been tampered with.

2.

Verify the digest listed in each entry in the
.SF file with each corresponding section in the
manifest.

The
.SF file by default includes a header
containing a hash of the entire manifest file. When
the header is present, then the verification can
check to see whether or not the hash in the header
indeed matches the hash of the manifest file. If
that is the case, verification proceeds to the next
step.

If that is not the case, a less optimized
verification is required to ensure that the hash in
each source file information section in the
.SF file equals the hash of its corresponding section
in the manifest file (see The Signature (.SF)
File).

One reason the hash of the manifest file that is
stored in the
.SF file header may not equal the
hash of the current manifest file would be because
one or more files were added to the JAR file (using
the
jar tool) after the signature (and thus the
.SF file) was generated. When the
jar tool is used to
add files, the manifest file is changed (sections
are added to it for the new files), but the
.SF file is not. A verification is still considered
successful if none of the files that were in the
JAR file when the signature was generated have been
changed since then, which is the case if the hashes
in the non-header sections of the
.SF file equal
the hashes of the corresponding sections in the
manifest file.

3.

Read each file in the JAR file that has an entry in
the
.SF file. While reading, compute the files
digest, and then compare the result with the digest
for this file in the manifest section. The digests
should be the same, or verification fails.

If any serious verification failures occur during the
verification process, the process is stopped and a
security exception is thrown. It is caught and displayed
by
jarsigner.

Multiple Signatures for a JAR File

A JAR file can be signed by multiple people simply by
running the
jarsigner tool on the file multiple times, specifying
the alias for a different person each time, as in:

jarsigner myBundle.jar susan
jarsigner myBundle.jar kevin

When a JAR file is signed multiple times, there are
multiple
.SF and
.DSA files in the resulting JAR file,
one pair for each signature. Thus, in the example above,
the output JAR file includes files with the following
names:

SUSAN.SF
SUSAN.DSA
KEVIN.SF
KEVIN.DSA

Note: It is also possible for a JAR file to
have mixed signatures, some generated by
the JDK 1.1 javakey tool and others by
jarsigner. That is, jarsigner can be used
to sign JAR files already previously signed using javakey.

OPTIONS

The various
jarsigner options are listed and described below.
Note:

Tag

Description

o

All option names are preceded by a minus sign (-).

o

The options may be provided in any order.

o

Items in italics (option values) represent the actual values
that must be supplied.

o

The
-keystore, -storepass, -keypass, -sigfile, and
-signedjar options are only relevant when signing a JAR file,
not when verifying a signed JAR file. Similarly, an alias is
only specified on the command line when signing a JAR file.

Tag

Description

-keystore url

Specifies the URL that tells the keystore location. This
defaults to the file
.keystore in the users home directory,
as determined by the
user.home system property.

A keystore is required when signing, so you must explicitly
specify one if the default keystore does not exist (or you
want to use one other than the default).

A keystore is not required when verifying, but if one is
specified, or the default exists, and the
-verbose option was
also specified, additional information is output regarding
whether or not any of the certificates used to verify the JAR
file are contained in that keystore.

Note: the
-keystore argument can actually be a file name (and
path) specification rather than a URL, in which case it will
be treated the same as a "file:" URL. That is,

-keystore filePathAndName

is treated as equivalent to

-keystore file:filePathAndName

-storetype storetype

Specifies the type of keystore to be instantiated. The
default keystore type is the one that is specified as the
value of the "keystore.type" property in the security
properties file, which is returned by the static
getDefaultType method in
java.security.KeyStore.

-storepass password

Specifies the password which is required to access the
keystore. This is only needed when signing (not verifying) a
JAR file. In that case, if a
-storepass option is not
provided at the command line, the user is prompted for the
password.

Note: The password shouldnt be specified on the command line
or in a script unless it is for testing purposes, or you are
on a secure system. Also, when typing in a password at the
password prompt, the password is echoed (displayed exactly as
typed), so be careful not to type it in front of anyone.

-keypass password

Specifies the password used to protect the private key of the
keystore entry addressed by the alias specified on the
command line. The password is required when using
jarsigner to sign a JAR file. If no password is provided on the command
line, and the required password is different from the store
password, the user is prompted for it.

Note: The password shouldnt be specified on the command line
or in a script unless it is for testing purposes, or you are
on a secure system. Also, when typing in a password at the
password prompt, the password is echoed (displayed exactly as
typed), so be careful not to type it in front of anyone.

-sigfile file

Specifies the base file name to be used for the generated
.SF and
.DSA files. For example, if file is
DUKESIGN, the
generated
.SF and
.DSA files will be named
DUKESIGN.SF and
DUKESIGN.DSA, and will be placed in the
META-INF directory of the signed JAR file.

The characters in file must come from the set "a-zA-Z0-9_-".
That is, only letters, numbers, underscore, and hyphen
characters are allowed.
Note: All lowercase characters will
be converted to uppercase for the
.SF and
.DSA file names.

If no
-sigfile option appears on the command line, the base
file name for the
.SF and
.DSA files will be the first 8
characters of the alias name specified on the command line,
all converted to upper case. If the alias name has fewer than
8 characters, the full alias name is used. If the alias name
contains any characters that are not legal in a signature
file name, each such character is converted to an underscore
("_") character in forming the file name.

-signedjar file

Specifies the name to be used for the signed JAR file.

If no name is specified on the command line, the name used is
the same as the input JAR file name (the name of the JAR file
to be signed); in other words, that file is overwritten with
the signed JAR file.

-verify

If this appears on the command line, the specified JAR file
will be verified, not signed. If the verification is
successful, "jar verified" will be displayed. If you try to
verify an unsigned JAR file, or a JAR file signed with an
unsupported algorithm (for example, RSA when you dont have an RSA
provider installed), the following is displayed: "jar is
unsigned. (signatures missing or not parsable)"

It is possible to verify JAR files signed using either
jarsigner or the JDK 1.1
javakey tool, or both.

For further information on verification, see JAR File
Verification.

-certs

If this appears on the command line, along with the
-verify and
-verbose options, the output includes certificate
information for each signer of the JAR file. This information
includes:

Tag

Description

o

the name of the type of certificate (stored in the
.DSA file) that certifies the signers public key

o

if the certificate is an X.509 certificate (more
specifically, an instance of
java.security.cert.X509Certificate): the distinguished
name of the signer

The keystore is also examined. If no keystore value is
specified on the command line, the default keystore file (if
any) will be checked. If the public key certificate for a
signer matches an entry in the keystore, then the following
information will also be displayed:

o

in parentheses, the alias name for the keystore entry
for that signer. If the signer actually comes from a JDK
1.1 identity database instead of from a keystore, the
alias name will appear in brackets instead of
parentheses.

-verbose

If this appears on the command line, it indicates "verbose"
mode, which causes
jarsigner to output extra information as
to the progress of the JAR signing or verification.

-internalsf

In the past, the
.DSA (signature block) file generated when a
JAR file was signed used to include a complete encoded copy
of the
.SF file (signature file) also generated. This
behavior has been changed. To reduce the overall size of the
output JAR file, the
.DSA file by default doesnt contain a
copy of the
.SF file anymore. But if
-internalsf appears on
the command line, the old behavior is utilized. This option
is mainly useful for testing; in practice, it should not be
used, since doing so eliminates a useful optimization.

-sectionsonly

If this appears on the command line, the
.SF file (signature
file) generated when a JAR file is signed does not include a
header containing a hash of the whole manifest file. It just
contains information and hashes related to each individual
source file included in the JAR file, as described in The
Signature (.SF)
File .

By default, this header is added, as an optimization. When
the header is present, then whenever the JAR file is
verified, the verification can first check to see whether or
not the hash in the header indeed matches the hash of the
whole manifest file. If so, verification proceeds to the next
step. If not, it is necessary to do a less optimized
verification that the hash in each source file information
section in the
.SF file equals the hash of its corresponding
section in the manifest file.

For further information, see JAR File Verification.

This option is mainly useful for testing; in practice, it
should not be used, since doing so eliminates a useful
optimization.

-provider provider_class_name

Used to specify the name
of the cryptographic service providers master class
file when the service provider is not listed in
the security properties file.

-Jjavaoption

Passes the specified javaoption string directly to the runtime system.
(jarsigner
is actually a "wrapper"
around the interpreter.) This option should not contain any
spaces.
It is useful for adjusting the execution environment
or memory usage.
For a list of possible flags, type
java -h or
java -X at the
command line.

EXAMPLES

Signing a JAR File

Suppose you have a JAR file named
bundle.jar and youd
like to sign it using the private key of the user whose
keystore alias is "jane" in the keystore named "mystore"
in the "working" directory. Suppose the keystore
password is "myspass" and the password for janes
private key is "j638klm". You can use the following to
sign the JAR file and name the signed JAR file
"sbundle.jar":

Note that there is no
-sigfile specified in the command
above, so the generated
.SF and
.DSA files to be placed
in the signed JAR file will have default names based on
the alias name. That is, they will be named
JANE.SF and
JANE.DSA.

If you want to be prompted for the store password and
the private key password, you could shorten the above
command to

s = signature was verified
m = entry is listed in manifest
k = at least one certificate was found in keystore

jar verified.

Verification with Certificate Information

If you specify the
-certs option when verifying, along
with the
-verify and
-verbose options, the output
includes certificate information for each signer of the
JAR file, including the certificate type, the signer
distinguished name information (if its an X.509
certificate), and, in parentheses, the keystore alias
for the signer if the public key certificate in the JAR
file matches that in a keystore entry. For example,

s = signature was verified
m = entry is listed in manifest
k = at least one certificate was found in keystore

jar verified.

If the certificate for a signer is not an X.509
certificate, there is no distinguished name information.
In that case, just the certificate type and the alias
are shown. For example, if the certificate is a PGP
certificate, and the alias is "bob", youd get

PGP, (bob)

Verification of a JAR File that Includes Idnetity Database Signers

If a JAR file has been signed using the JDK 1.1
javakey tool, and thus the signer is an alias in an identity
database, the verification output includes an "i"
symbol. If the JAR file has been signed by both an alias
in an identity database and an alias in a keystore, both
"k" and "i" appear.

When the
-certs option is used, any identity database
aliases are shown in square brackets rather than the
parentheses used for keystore aliases. For example: